Control system



1941- r w. D. COCKRELL 2,264,873

CONTROLSYSTEM Filed July 13, 1940 Fig I.

SCANNING UNIT vInventor"- William D. Cockr'ell,

b jg 6. Himtor'neg.

; Patented Z 1841 m3 OONTIOLSYB'III WiIIsnnm,N.!.a-Ignor m serpentine!Ge-calm New! mun-momma. Sari-($845,421

Thisinventionrelatestoqntrolsystmmm'e afteraintervllottime.

More the inventim relates to a timedelaydevlceoi'thecharacterdescribedinwhichthetimeintervalhmvenely tothespeedotamoviimelementminusaflxed time.

Oneapplicaflonotadeviceoithischaracterisiisuseinwithaphotoelectricdevice fordetectlngandmarkingflielocationofinholesinasteelstrip. InthispinholedetectorapplicatiomthesheetismarkedbyamagnetimbinwhichTrepresentsthetimedelay,Srepresenisthespeedandxandaareconstants.

Incarryingtheinventionintoeflectinone form thereof, the time inverselyproportional to speedminustheflxedtimeisobtainedby charging a capacitorwith a constant current the value of which is proportional to the speedof amoving element and adding to the voltage of the capacitor a voltageproduced by this charging current flowing through a resistor. Thecircuit is arrangedsothatwhenthesumoithese twovoltages attains apredetermined value, a controlling operation is initiated.

Inillustratingtheinventioninonetormthereof, it is shown as anhodied in aphotoelectric pinhole detecting and marking device. It will heunderstood, however, that the invention has other applicatimn.

For a better and more complete oftheinvenflcn,reterence shouldnowbehadto the foilowim speciiicatim md to theaccommnyinsdrawiminwhichl'lg.lisaslnmle,diagrammaflcal sketch 0! an t ofthe inventIm,andHg.2 isadisgrammaflcviewin perspective illustrating an'application at the invention.

lightsource lamps ll andlens system. 'lhelower box contains thephotoelectric cells, amplifiertubesandassociatedcircuitsmountedonapanel.Alenssystemsimilartothatintheupper boxis alsoprovided. Thescanneris qinpcdwitha pair of shutters (not shown) which provide for operation withany width of strip within predetermined limits. The structural details01 the scanner do not constitute any part of the present invention.Scanning units of this character are well \mderstood devices. They areprocurable upon the market and are described in printed publications andpatents. For example, a scanningunitoithischaracterisdescribedinUnitedStates Patent No. 2,193,590 Gulliksen. It is sutflcient to understandthat when a pinhole in the strip passu through the scanner, an impulseof positive voltage is applied to the conductor It,

i. e. the potential of conductor It becomes positive with respect to thenegative side ll of the direct-current source l5, I for a fewthousandths of a second. This signal voltage sets the device inoperation.

A magnetic marking device I1 is mounted a short distance away from thescanner in the direction of the travel of the strip and near the edge ofthe strip. This marking device serves to place a mark on the edge of thestrip when a pinhole hasbeen detected. Normally,the'solethecathodeisconnectedtothenegaflvesideli oithesource.Thescreengridli-isconnectedtotheposiflvesideoithesourceandisthmgivenapositivebiaaandgrldlhisconnectedthroughresistor litothenegativeside ltofthesource.

I6 Thuatbeccntmlgridllsisatthecathodepo tential and consequently thetube is normally conducting and solenoid i1 is normally energised.

Atwin triode electric valve II isalsoconnected across the source II, It.This valve is normally biasedthroughtheanode resistorllandthegridvoltagedivider resistors I2 and 23 so that the gridbias as measured betweenpoints 22. and 24 is approximately zero. and therefore the total tubecurrent flows through the left-hand path of the triode and throughitscathode resistor 25. A resistor 21 and a capacitor 2h are connected tergenerator 3|, resistors 32 and It and capacitor 34. Other types of tubeswith high transconductance would be. equally as satisfactory as electricvalve 2'. Tachometer generator ii is driven from the rolls II andconsequently it generates a voltage proportional to the speed of thestrip which is applied to the grid of valve 2. The positive terminal ofthe generator is connected to the grid.

A current. that is very closely proportional to the strip speed iscaused to flow in the circuit of electric valve 26. The current ismaintained constant for any given tachometer generatorv voltage becauseany tendency for the current to change such as caused by a variation inanode voltage is accompanied by a change in the volt-' age drop acrossresistors 28 and 20. This change in the voltage drop across theseresistors is applied to the grid and produces a current change in theopposite direction. The overall result is that the current is maintainedsubstantially consteady state condition,

-is approximately at; cathode potential which across source I, It tofilter the voltage supplied causes the valve to conduct. This results inpractically short circuiting the timing capacitor 34 andin maintainingthe voltage across the capacitor at'a very low value.

A thyratron tube a is also connected across conductors. ii, I. ResistorI! is connected between the anode and the side it of the source,

and the cathode is connected through resistors 40, ll and'voltagedivider resistor 42 to the negative side It of the source. Normally, thethyraunderstood from the following description.

When a pinhole in the strip passes through the photoelectriccell-detecting unit If, light falls for a brief instant of time on oneof thephotoelectric cells. This produces an electrical impulse, i. e. asudden positive variation in the voltage between it and the negativeside It of the source which is applied to the grid of the thyratron IIand as a result'thethyratron becomes conducting. 'From'the time thelight falls on the photoelectric cell until the thyratron becomesconducting is so brief that the two events occur practicallysimultaneously. When current passes through the voltage droppingresistor It, the voltage of the junction point lti'drops from its normalsteady state value to a very low value. For example, the steady statepotential of this point may be 300 volts and I when the current isflowing, the potential may stant for" a wide range of anode voltages andacross resistors II and It, and this has the effect.

of extendingv the linear variation of the tube current to low values oftachometer voltage.

Capacitor 36 and resistor 30 act as a filter to smooth out any ripple inthe voltage of the tachometer generator such as might be produced by itscommutator.

' Capacitor I4 is the timing capacitor which is charged by the constantcurrent supplied by electric valve 28. This same charging current alsoflows through the fixed resistor 33 and the adjustable resistor 32 toprovide the voltage which is added 'to thevoltage of the capacitor tocompensate for the fixed time of the operation of the marker; Since theactual operating speeds of different markers vary, the adjustableresistor 32 is provided to adjust the circuit accurately when theinstallation is completed.

An electric valve 31 is connected in parallel with capacitor 34; i. e.its anode is connected to one terminal of the capacitor and the cathodeto the other. -This valve is preferably of the "beam" or pento'de typein which the anode may operate successfully at a minimum voltageposidrop to a value of less than 20 volts.

This resultant potential change is transferred to the timing circuitthrough the capacitor 48. More specifically, the decrease in voltage ofpoint It allows capacitor I! to discharge with the As the capacitor 34becomes charged, the voltage across the capacitor increases and as thisvoltage increases, the voltage of the junction point 32a also increases.After an interval of time which is inversely proportional to the speedoftachometer generator 3| minus a fixed time, the voltage of the gridII. to which the point 32. is connected attains a'value at which theright-hand path of the valve 2| begins to conduct and causes current toflow through the resistor 2|. As a result of this the voltage of point2i. which is connected to grid 20 is decreased to such an extent thatthe left-hand. path of valve II ceases to conductcurrent. and thecurrent of the left-hand path is transferred to the right-hand path. Asaresult of the large j current which now flows through resistor 2|, the

' voltage of point Ilsis suddenly decreasedto a 'thegrid'lta of. valveII. As a voltage of grid lls becomes so negativewith man its cathodethat valve; ll ceases to conduct curtive with respect to the cathode. Inthe normal 78 rentv and the solenoid II of-the marker is deenergized.After the fixed time required for the marker element l1 to drop to thestrip, the surface of the strip is suitably marked as by hiuriing at theedge oi! the strip. 11 all the adjustments. have been properly made, themark will be made at a distance from the detector equal to the distanceof the pinhole from the detector so that the pinhole may be readiilocated.

That the time interval interposed by the timing circuit between thesignal voltage and the deenergimtion of valve It to release the markeris inversely proportional to the speed of the strip minus a fixed timemay be demonstrated mathematically as follows:

Let

e=the voltage across resistors 32 and 33 an capacitor 3,

E=the tripping voltage, i. e. the grid voltage required to render theright-hand path of valve II conducting,

S=speed of the tachometer generator Si or the speed of the strip ll,

R=ohmic resistance of resistors 32 and 33,

C=capacitance oi capacitor II.

Then,

(l) 1:115 in which i is the constant current from valve 26 which chargescapacitor 34 and N is a constant.

Consequently for the time T to trip at a fixed limit voltage E,

E R ""c1 and substituting from (i) E R cNs fi SinceE,R,CandNareconstants is also a constant==K and Thus K In other words, Tis a time which is inversely proportionaltothespeedofthestrlpminusafixed time.

At the instant of the removal of voltage from marker solenoid I'l,voltage is also removed from the coil of "rese relay 5. Relay I5,however, does not drop out instantly because of the capacitor 46 whichis connected across its coil. The brief interval during which the resetrelay is held picked up is suiiicient to permit the plunger of themarker solenoid to drop out completely before the reapplication ofpower.

When the contacts a oi relay do open, and

39. regains the positive potential of the side l5 oi the source. As aresult, capacitor 43 is subjected to a greatly increased voltage andcharges rapidly. This causes the voltage of the grid 81. of valve 31 tobecome more positive, thereby to render the valve 31 conducting so thatcapacitor ll is again short circuited and thereby rapidly discharged.The resulting decrease in voltage across the capacitor 34 causes thepotentials of the point 32. and of the grid 20. of valve 2| to becomeincreasingly negative with the result that the right-hand path 01' valve2| becomes nonconducting.- The interruption of current in the right-handpath of valve 2| causes the IR drop acrossresistorsfl andtodisappearsothat the potential of point'll. attains a high positivevalue, thereby increasing the voltage across capacitor 4|. As capacitor44 charges, the grid b of valve ll becomes increasingly positive so thatthe left-hand path 01 valve 2| again becomes conducting. Simultaneously,the voltage of grid Ila becomes more positive and causes interrupt theanode circuit of the thyratron 3 8,

the thyratron becomes non-conducting. Resistor l1 and capacitor 48 forma highly damped oscillatory circuit to insure the positive circuit breakand minimum surge on remake. In responsetotheinterruptionotcm'rentintheanode-cathode circuit of thyratron a, the m drop'acros resistor itdisappears, and point the valve ll to become conducting, thereby toenergize the marker operating solenoid l! to retract the marker and alsoto energize solenoid 45 of the reset switch which thereupon recloses itscontacts 45-. This terminates one complete timing cycle, and the systemis now in its steady state condition and is thus reset for a subsequentoperation.

Resistor 29 is made adjustable to provide a means for varying thecharging current for a given tachometer voltage. The resultant variationin the time delay in the operation of the marker mam it possible to usethis control for adjusting the distance that the pinhole will moveforward beiorethestripm marked.Thisisdesirablebecauseitpermitsthemarkertobeinstalledatvariousdistancesi'rmnthescanner.

Although in accordance with the provision of the Patent statuts th'minvention '3 as embodied in concrete form and the principlethereothasbeendescribedtogetherwiththebest mode in which it is nowcontemplated applying thatm'lnciplaitwillbeunderstoodthattheapare merelyillustrative and that the invention is not limited thereto, sincealterations and modifications will readily suggest themselves to personsskilled in the art without departing from the true spirit of thisinvention or from the scope of the annexed claims.

What I claim as new and desire to secure by letters Patent of the UnitedStates is:

1. A device for producinga time delay inversely proportional to thespeed of a movin element minus a fixed time comprising an electricalenergy storage device, means responsive to a signal for initiating thesupply of current to said energy storage device, means for maintainingsaid current substantially constant at a value proportional to saidspeed, means for supplying a voltage pr p rtional to said fixed time tothe circuit of said energy storage device, and means responsive to thesum of said voltage and the voltage across said energy storage devicefor initiating a controlling operation when the sum of said voltagesattains a predetermined value.

2. A device for producing a time delayinverselyproportionaitothespeedoiamovingelementminusafixedtimecomprisingasubstantially discharged capacitm', meansmponsiye to a sigml for initiating the supply of current to saidcapacitor to increase the voltage acres said capacitor, means formaintainin said current conspacers stant at a value proportional to saidspeed.

said capacitor thereby to increase the voltage across said capacitor.means for maintaining said current constant at a value proportional tosaid speed, means for supplying a voltage.proportionaltosaidfixedtimetothecircuitoi'said capacitor, and meansresponsive to the sum of said voltages for initiating a controllingoperation when the sum of said voltages attains a predetermined value.

4. A device for initiating a controllingoperationinresponsetoasignalanintervalottime' after said signal that isinversely proportional tothespeed ot amovingelementminusafixedtimecomprisingacontrolcircuitanelectrical energy storage deviceconnected in said circuit, means for short circuiting said energystorage device prior to said signal, means-tor introducingavoltageinsaid circuitproportionaltosaidfixed time. means for causing acurrent to fiow in said circuit proportional to the speed of saidelement,

means responsive to said signal for interrupting the shortcircuit aboutsaid energy storage device thereby to cause said current to storeelectrical energy in said storage device and to produce an increasingvoltage across said storage device, and means responsive to the sum ofsaid voltages for initiating said controlling operation when said sumequals a predetermined value.

5. A device for initiating a controlling opera-' tion in response toasignal an interval of time after said Si nal Prop rtional to the speedof a moving element minus a fixed time comprising a.

control circuit, a capacitor connected in said circuit, means forcausing a current to fiow in said circuit, means for short circuitingsaid capacitor.

prior to said signal, means for introducing a voltage in said circuitproportional to said fixed time, means responsive to said signal forrendering said short circuiting means ineiiective, means for maintainnigthe current in said circuit substantially constant at a valueproportional to the speed of said element so that the voltage acrosssaid capacitor is caused to increase, and means ing a controllingoperation when said sum equals a predetermined value.

7. A control system for initiating a controlling operation in response,toa signal a time interval'aitersaldsignalthatisllroportionaltothespe'ed,

of a moving element minus afixedtime comprising a control circuit, acapacitor and an adjus able resistor connected in series. relationshipin said circuit. means for causing a current to now: in said circuit.means for short circuiting said.

capacitor prior to said sig means for maintaining the current in saidcircuit substantially constant at a fixed value proportionalto the speedoi said element, said resistor being ad- Justed so that the voltage dropacross said resistor is proportional to said fixed time, meansresponsive to said signal for rendering said short circuiting meansinefiective whereby said capacitor is charged and the voltage acrosssaid capacitor is increased. and means for initiating a controllingoperation when the sum oi said voltages attains a predetermined valuecomprising a second control circuit including an electric valve havingits grid circuit connected acrosssaid cspacitor and said resistor.

' 8. A time delay device comprisingvin tion a control circuit, acapacitor and a resttor included in said circuit, means for causing acurrent to fiow in said circuit, an electric valve connected across saidcapacitor, control means for rendering said valve conducting therebytosh'ort circuit said capacitor, means including a tachometer generatorconnected in said circuit for maintaining the current in said circuitsubstantially constant at a value proportional to the speed or saidgenerator, means responsive to asignal for rendering said shortcircuiting means ineflective whereb said capacitor is charged and thevoltage 7 across said capacitor is increased, and means mined value.

means responsive to a signal for rendering said responsive to the sum ofsaid voltages for initiating a controlling operation when said sumattains a predetermined value.

6. A' control system for initiating a controlling operation in responseto a signal an interval of time alter said signal proportional to thespeed oi a moving element minus a fixed time comprising a controlcircuits capacitor in said circuit. a resistor connected in series withsaid capacitor, means for causing a current to fiow in said circuit,means for short circuiting said capacitor v prior to said signal, meansresponsive to said signal for rendering said short circuiting meansineii'ective, means for maintaining the current oi saidcircuitsubstantially constant at a value proportlonal to the speed ofsaidelement whereby the voltage across said capacitor is increased, andmeansresponsive to the sum of the voltages across said capacitor andsaid resistor tor initiatresponsive to the sum of the voltages acrosssaid capacitor and resistor for initiating a controlling operation afteran interval oi time required tor the sum of said voltages to attain apredeter- 9. A time delay device comprising in com tion a controlcircuit, a capacitor and an adiust- V able resistor included in saidcircuit, means for ing an electric valve and'a tachometer generatorincluded in said circuit for maintaining the current in said circuitsubstantially constant at a value proportionalto the speed of saidgenerator,

short circuitingmeans inefiective -so that. said capacitor is chargedand the voltage across said capacitor is increased, and means responsiveto the sum of the voltages acrosssaid capacitor and resistor forinitiating a controlling operation after an interval of time requiredfor the sum of said voltages to attain a predetermined-value.

10. A time delay device comprising in combina-' tion a control circuit.a capacitor and a resistor included in said circuit, means for causing acurrent to flow in said circuit, a first electric valve connected inparallel with said capacitor and connected to be conducting i'orshortcircuiting said capacitor, means for maintaining the current in saidcircuit substantially constant at a value proportional to the speed oi amoving element, a second electric valve connected to be non-conducting,means for applying .a signal,

voltage to the grid oi said non-conducting valve to render said valveconducting, means including a connection from the anode-cathode circuitof said second valve to the grid circuitofsaidfirst 2,264,873 valve forrendering said first valve non-conducting so that said capacitor ischarged and the voltage across said capacitor is increased, meansresponsive to the sum of the voltages across said capacitor and resistorfor initiating a controlling operation after a time interval requiredfor the sum or said voltages to attain a predetermined value, and meansresponsive to said controlling operation for rendering said second valvenonconducting thereby to reset said time delay device for a subsequentoperation.

11. A time delay device comprising in combination a control circuit, acapacitor and a resistor connected in said circuit, a first electricvalve connected in parallel with said capacitor, means for applyingvoltage to the grid of said valve to render it conducting thereby toshort circuit said capacitor, a second electric valve, means forapplying a voltage to the grid oi! said second valve to render saidsecond valve non-conducting, means for applying a signal voltage to thegrid 01' said second valve to render said second valve conducting, aconnection from the anode-cathode circuit of said second valve to thegrid circuit of said first valve for rendering said first valvenonconducting in response to current in the anode cathode circuit oisaid second valve thereby to cause said capacitor to be charged and thevoltage across said capacitor to increase. and electric valve meansresponsive to the sum of the voltages across said capacitor and resistorfor initiating a controlling operation after an interval oi time. I

requiredtorth'esumotsaidvoltagestoattaina predetermined value.

12. A control system for initiating a controlling operation in responseto a signal an interval of time after said signal proportional to thespeed of a moving element minus a fixed time comprising a controlcircuit, a capacitor and a first adjustable resistor included in saidcircuit, means including a first electric valve included in said circuitfor controlling the current in said circuit, means comprising atachometer generator driven by said element and a second adjustableresistor connected in the anode-cathode circuit oi said valve and aconnection from said anode-cathode circuit to the grid of said valve formaintaining the current in said control circuit substantially constantat a value proportional to the speed of said element, said firstresistor being adjusted to a value such that its voltage drop isproportional to said fixed time, a second electric valve having itsanode-cathode circuit connected in parallel with said capacitor, meansfor applying a voltage to the grid circuit of said second valve torender said second valve conducting thereby to short circuit saidcapacitor, means for applying a signal voltage to the grid circuit orsaid second valve thereby to render said second valve non-conducting sothat said capacitor is charged and the voltage across said capacitor isincreased. and means responsive to the sum or the voltages across saidcapacitor and first resistor for initiating a controlling operation whenthe sum of said voltages attains a predetermined value.

WHLIAMD.COCKRE[L.

